Direction finder system



Nov. 29, 1949 E. COLE DIRECTION FINDER SYSTEM Filed Jan. 4, 1947INVENTOR. EUGENE 00L A TTORNEY Patented Nov. 29, 1949 UNITED STATESPATENT OFFICE DIRECTION FINDER SYSTEM Eugene Cole, Long Island, N. Y.,assignor to Federal Telecommunications Labs. Inc., New York, N. Y., acorporation of Delaware Y Application January 4, 1947, Serial No.720,155

Claims. (Cl. 343-117) This invention relates to automatic indicatingdirection finders, and particularly the type providing control of theamplitude of the sense voltage during bearing seeking operation.

Direction finders of the type using rotating loop antennas or xed Adcockantenna arrays are well known. In order to resolve the 180 senseambiguity which is commonly associated with the use of these antennas, asense antenna, usually of the vertical omni-directional type, isprovided. In one instance employing a fixed Adcock array having anomni-directional reception pattern, a sense antenna is adapted to beyswitched in to the bearing translating device for altering theomni-directional pattern to a cardioid shaped pattern. The use of thecardioid shaped pattern during bearing seeking operation enables theresolving of the 180 sense ambiguity of this system.

One of the objects of this invention is to provide an improved sensingsystem for direction nders and more particularly one which is automaticin operation.

Another object of this invention is to provide automatic means forcontrolling the sense voltage particularly its magnitude used inresolving 180 sense ambiguity of direction finder systems.

Another related object of this invention is to provide automatic meansfor improving the sensitivity of the direction finder about the zero ornull indication.

In a preferred embodiment of the present invention low frequency signalsare separately mixed with the signals received from a loop antenna and asense antenna. Means are further provided for using the low frequencysignals after detection in a radio direction finder receiver coupled tothe antenna system for controlling the sense voltage applied to thebearing resolving system.

The above mentioned and other features and objects of this inventionwill become more apparent and the invention itself, though notnecessarily del-ined by said feature and objects, will be bestunderstood by reference to the following descripton of an embodiment ofthe invention taken in connection with the single figure of the drawing,wherein there is shown a block circuit diagram of an automatic directionnder sense control system employing modulation and embodying theinvention.

The single figure shows a low frequency oscillator I arranged to supplyvoltage to a pair of radio frequency modulators 2 and ,3, Thesemodulating voltages are applied in phase opposition through transformer4 to the secondary control elements 5 and 6 of tubes 2 and 3respectively. The radio frequency voltages from the radio direction nderloop 'I are applied, in phase opposition, to the primary controlelements 8 and 9 of tubes 2 and 3 respectively. The plates of tubes 2and 3 are coupled in parallel such that their plate currents areadditive and connected to a common load I0. Under these conditions acarrier suppressed modulated wave is produced. The voltages developedacross the load I0 are then passed to a conventional receiver II where atone, preferably audible is produced. The frequency of this tone will betwice the frequency of the low frequency oscillator modulator I.

An amplifier l2 is also connected to the common load I Il. The gridvoltage of amplifier I2 is supplied by the sense antenna I3 which iscoupled to the primary control element I4. The sense antenna voltage,and the loop voltage developed across the loop tuning condensers I5 andI6 will normally be in phase or out of phase dependent on which end ofthe loop is being considered, and therefore affords means for resolvingthe sense ambiguity.

For convenience it is assumed that tubes 2, 3 and I2 have equalamplification for the radio frequency voltages. Now if the sense voltageis equal to or greater than the loop voltage, the voltage being fed tothe receiver will be the conventional amplitude modulated wave enablingthe resolving of sense ambiguity. The tone and the output of thereceiver will now be of the same frequency as the modulator I.

Expressing these relations:

The involtage induced in the loop is EL=h cos 0 (sin wit) where h equalsthe effective height of the loop; 0=angle of arrival of electromagneticwave; sin wt=arriving wave;

The voltages appearing at 8 and 9 across the tuning condensers I5 and I6are:

The voltage induced in the vertical or sense antenna I3 is E13=A2h/2 sinwit Replacing the expressions A171/ 2 and Aan/2 with constants V1 and V2respectively, the contribu- 3 tion of tubes 2, 3, and 4 to the load I0for a modulating voltage of sin (wzt) and sin (wat) is E2=V3 sin w2l(V1COS 0 sin wit) The contribution to the receiver I I is This is theexpression for a conventional .amplitude modulated wave. The modulationwill be maximum when -g-2= ViVg cos 0 (100% modulated Wave) Where V1, V2are constants as specified above and V3 is a constant dependent upon E2and E3.

Under normal operational conditions the maximum amplitude of themodulation component attainable at rthe receiver output is proportionaltothe cosine of the angle of arrival 0. This means that a variation invamplitude of zero to some other arbitrary value exists. In ordertosharpen the indication about the zero or null-position, some sort .oflimiting action 'is desirable. If the indicator operationis confined sothat it responds only .to signals of the samefrequency as oscillator 1this limiting action can be arranged. In this connection there is.provided an isolating ampliiler ,ITI .coupled to a diode detector I8through `a narrow .band-pass Afilter .L9 designed to pass the frequencyof oscillator I. The diode I provides negative voltage .proportional tothe signal amplitude, The gain of tube I2, preferably of the variablemutype pentode, is controlled by applying .the potential from diode I8 tothe .primary control element I4 through connection 2i).

-As the loop becomes oriented -to the null or zero .indication of theincoming radio frequency signal the negative voltage applied to thecontrol element I4 of .tube I2 is .decreased proportionatelyresultin gina greater .amplification of the sense voltage used for .mixing withthe loop volt- :ages .across the -load l0. This results in produc- `ingsteeper slope to the null portion of .the Ydirection .finder receptionpattern signals which are .applied to receiver VI-I and results .in amore vprecise bearing indication. As .the direc-tion finder .antennasystem approaches the bearing, the indication is sharpened :about .thenull position.

The input to .the detector |-8 is :also passed to a control circuit 2|,zand may be .used for controlling the orientation Lof loop antenna ll.This control can .take several forms, vas for example, a visualindicator 23, an audio indicator or a control circuit of an :automaticnull-seeking direction finder wherein the amplitude of the signal asreceived in the control circuit 2! controls motor 24 for rotating theloop 1.

If the control voltage from .the output of the diode detector I8 is onlyapplied to the primary .control .element of .only tubes 2 and 3simultaneously through connection 22, a `further advantage is attained.It is then possible to operate a bearing indicator in the controlcircuit of an automatic direction finder lsystem Without appreciablyimpairing the audibility of modulated signals. Since the indicatoroperates von a fixed frequency, the sensitivity of the indication may beincreased a factor proportional to the ratio of .the audio response bandwidth to the indicator .channel band width. This factor can readilyexceed 20 db. If the sensitivity of the indicator and audio reproducerare of the same order, the modulation products produced by the loopmodulators may be reduced by 20 db. or more while maintaining the samesignal to noise ratio at the indicator as exists in the reproducer. If aswitch 23 located in the coupling network between said diode I8 and thesaid controlconnection, is closed, this direction finder automaticvolume control action may be eliminated, as by short-circuit `:therebymaking it an optional feature in an automatic direction finder.

While Ihave described above the principles of my invention in connectionwith specific apparatus and kparticular modifications thereof, it is tobe .clearly :understood that this description is made only by way ofexample and not as a limitation of the scope of my invention.

1. A radio direction i'lnder having means to receive component energiesof directional and omni-directional patterns and to produce therefrom `aresultant energy reception pattern for determining the bearing ofreceived .radiant energy, comprising means to derive from said resultanta control energy and -means for applying said control .energy to the.means for receiving the energy of .one .of said components whereby thedirectivity of .said resultant pattern is continuously varied :as saidbearing is approached.

2. In a radio .direction finder .system of the type comprising an`effectively.rotating directional antenna and a sense antenna, a signalsource of given frequency, means for .mixing signals from said sourceand the electrical signals received by said directional antenna, means.for combining said mixed signals with the signals from saidsense-antenna, means for demodulatingsaid combined signals, means fortranslating Ysaid demodulated signals to obtain the .direction ofreceived electrical signals, ymeans for producing a bias signalcorresponding to the amplitude of said demodulated signals, said biassignalcontrolling the relative intensities of :the signals from saiddirectional and sense antennas whereby the sensitivity of saidtranslating means is increased about .the null `position .of thecombined antenna reception pattern.

3. A radio direction nder system comprising an effectively rotating-directional antenna, a sense antenna, a Ilovv `frequency signal source,means for mixing said low frequency signals and the electrical signals`received by said directional antenna, means for combining the signalreceived by said sense antenna and said mixed signals, mea-ns ford-emodulating said combined signals, means for deriving from saiddemodulated signal a control energy for effectively controlling therotation of said directional antenna, means for producing a bias signalcorresponding to the amplitude of said demodulated signals, meansresponsive to said bias signal for controlling the .relative intensityof said directional and sense *antenna signals before combining wherebythe sensitivity of said control means is increased .about the nullposition fof vthe antenna reception pattern.

4. A radio direction finder system comprising .an effectively rotatingdirective antenna, a sense antenna, a loW frequency signal source, means.for mixing said 10W frequency signals and the electrical signalsreceived by said directional antenna, means for combining the signalreceived by said .sense antenna and .said mixed signals, means fordemodulating said combined signal means responsive to said demodulatedsignals for effectively controlling the rotation of said directionalantenna, means for producing a bias signal proportional to the amplitudeof said demodulated signals means responsive to the value of said biassignal for controlling the amplitude of said sense antenna signal formixing with said low frequency signals to vary inversely with theamplitude of said demodulated signals.

5. A radio direction finder comprising an effectively rotatingdirectional antenna, a sense antenna, a source of low frequency signals,a rst and second mixing circuit, and a receiver, means for modulatingthe electrical signals received by said directional antenna comprisingsaid low frequency source and said first and second mixer circ-uits,means coupling the output of said first and second mixers to saidreceiver whereby carrier suppressed low frequency modulated electricalsignals are produced in said receiver, a third mixer circuit, means forcoupling the electrical signals received by said sense antenna throughsaid third mixer to said receiver, said receiver comprising means fordemodulating the signals applied thereto for obtaining said lovTfrequency signals, means for eiiectively controlling the rotation ofsaid directional antenna, means for applying said demodulated signals tosaid controlling means, means for producing a bias signal proportionalto said demodulated signals, means for applying said bias signal to saidthird mixer circuit whereby the amplitude of said sense antenna signalapplied to said receiver varies inversely proportionally with theamplitude of said demodulated signals.

6. In a radio direction nder of the type comprising an effectivelyrotating directional antenna and a sense antenna, a source of electricalsignals of given frequency and a receiver, a rst and second mixingcircuit, means for modulating the the electrical signals received bysaid directional antenna comprising said given frequency source and saidfirst and second mixer circuits, the output of said first and secondmixing circuits comprising carrier suppressed given frequency modulatedelectrical signals, means for applying said last named signals to saidreceiver a third mixing circuit, means for coupling the electricalsignals received by said sense, means for coupling the electricalsignals received by said sense antenna through said third mixing circuitto said receiver, said receiver comprising means for demodulating thesignals applied thereto for obtaining said given frequency signals atranslating means and means for applying thereto said demodulatedsignals whereby the direction of antennae received electrical signals isdetermined, means for producing a bias signal corresponding to saiddemodulated signals, means for applying said bias signals to said rstand second mixer circuits whereby the sensitivity of said translatingmeans is increased about the null-position of the reception pattern ofsaid directive antennae.

7. A radio direction finder comprising an effectively rotatingdirectional antenna, a sense antenna, a receiving means, a source ofgiven frequency signals, a rst and second mixing circuit, means formodulating the electrical signals received by said directional antennacomprising said low frequency source and said iirst and Second mixercircuits the output of Said rst and second mixers being electricallycoupled to said receiving means whereby carrier suppressed low frequencymodulated electrical signal-s are passed to said receiving means, athird mixer circuit, means for coupling the electrical signals receivedby said sense antenna through said third mixer to said receiving means,said receiving means comprising means for demodulating the signalsapplied thereto for obtaining said given frequency signals, meansresponsive to said demcdulated signals for eiectively controlling therotation of said directional antenna, means for producing a bias signalproportional to said demodulated signals, means for applying said biassignals to said first and second mixer` circuits whereby the sensitivityof said control means is increased about the null-position of thereception pattern of said directive antenna.

8. In a radio direction finder system of the type comprising aneffectively rotating directional antenna, and sense antenna, a receivingmeans, a rst and second electron discharge device, having controlelectrodes, means for applying modulation signals from said givenfrequency signal source in phase opposition to control eleotrodes ofsaid first and second device, means for applying electrical signalsreceived by said directional antenna in phase opposition to controlelectrodes of said rst and second device means for coupling the outputof said first and second device to said receiving means, a thirdelectron discharge device having control electrodes, means for couplingthe electrical signals received by said sense antenna to a controlelectrode of said third device, means for coupling the output of saidthird device to said receiving means, an amplifier circuit coupled tothe output of said receiving means, said amplifier circuit having itsoutput coupled through a band pass lter to the input of a detectorcircuit, said band pass filter being tuned i0 pass said given frequencysignals from said receiving means. means for translating said filteredsignals to obtain the direction of received electrical signals, meansfor applying the output of said detector to control electrodes of saidfirst and second device whereby the sensitivity of the direction finderis improved about the null-position of the reception pattern of saiddirectional antenna.

9. In a radio direction nder system of the type comprising aneffectively rotating directive antenna and a sense antenna a source ofxed frequency modulation signals, a receiving means, a rst and secondelectron discharge device, having control electrodes means for applyingmodulation signals from said fixed frequency source in phase oppositionto control electrodes of said first and second device, means forapplying electrical signals received by said directional antenna inphase opposition to control electrodes of said rst and second device,means for coupling the output of said first and second device to saidreceiving means. a third electrical discharge device, having controlelectrodes means for coupling the electrical signals received by saidsense antenna to a control electrode of said third device, means forcoupling the output of said third device to said receiving means anamplier circuit coupled to the output of said receiving means, saidamplier circuit having its output circuit coupled through a band passfilter to the input of a detector circuit, said band pass ilter beingtuned to pass said xed frequency signals, from said receiving means,means responsive to said band pass filter output for eiectivelycontrolling the rotation of said omni-directional antenna, means forapplying the output of said detector to control electrodes of said rstand second device whereby the sensitivity of the direction nder isincreased, about the null-position of the reception pattern of saiddirective, antenna.

10.-In a. radiodirection nder system of the typecomprisingl aneffectively rotating directive antenna, and. a. sense antenna, a sourceof low frequency' modulation` signals, a receiving means arst; andsecond electron discharge device, having control electrodes, means forapplying modulation signals from said low frequency source in phaseopposition to control electrodes of said rst and second` device, meansforl applying electrical signals received by said direc-tional antennain phase opposition to control electrodes of said rst and second device,means for coupling the output ofr said rst and. second dev-ice to saidreceiving means, a third electron discharge device having controlelectrodes means for coupling the electrical signals received by saidsense antenna to acontrol electrode of said third device, means forcoupling the output of said thirdv device to said receiving means, anamplifier circuit coupled: toy the output of said receiving means, saidamplier circuithaving itsoutput circuit coupled through a band. passlter to theinputof a detector circuit, said band pass filter being tunedto pass said low frequency signals from said receiving means, meansresponsive to saidV band passl lter output for effectively controllingthe rotation of said directive antenna, the output of said detectorbeing coupled to a control electrode of said third device whereby a biassignal is produced, said bias signal controlling the amplification ofsaid third device whereby the sense antenna signals applied to saidreceiving means vary in accordance with said receiving means output.

EUGENE COLE.

REFERENCES CITED The following references are of record. in. the le ofthis patent:

UNITED sTATEs i=ATENTs Number Name Date 2,171,561 Hooven Sept. 5, 19392,220,904 Hooven Nov. 12, 1940 2,314,029 Bond et al Mar. 16, 1943

